1. Field of the Invention
The present invention relates to a liquid ejection apparatus and a resist pattern forming method, and more particularly, to resist patterning technology used when forming a wiring pattern on a printed wiring substrate.
2. Description of the Related Art
Photolithography is generally used as a method of manufacturing a print substrate. In photolithography, a resist layer is formed by using dry film resist or liquid resist on copper-clad laminate constituted by an insulating layer and a copper cladding layer made of copper foil, the resist layer is exposed in a pattern by being irradiated with ultraviolet light through a photo mask, and then development is carried out, thereby achieving patterning of a resist pattern. Thereupon, the copper foil which is not covered by the resist is removed by etching, thus obtaining a desired conductor pattern. The foregoing description relates to a subtractive type of photolithography technique, but in semi-additive or additive photolithography techniques, in a similar fashion, a photo resist is patterned in order to serve as a plating mask.
When forming fine circuits by means of subtractive lithography, there is narrowing of the image lines caused by side etching of the metal conductive layer, and the like, and hence this method is not necessarily advantageous for creating fine circuits. An additive method, on the other hand, is beneficial for creating fine circuits, but since all of the metal conductive layers are formed by electroless plating, then the manufacturing costs are high. A semi-additive method involves a large number of steps, but it is excellent for use in manufacturing fine circuits since it enables the use of electroplating, which allows high-speed operation. In the photolithography method described above, the manufacture of the photo mask takes time, and a developing step is required in the resist patterning process, which means that both time and costs become an issue. Furthermore, there is a problem of the disposal of waste solution from the developing step.
In response to this, a method has been proposed in which a pattern of resist material is created directly by means of an inkjet type system. In other words, a desired resist pattern is recorded directly onto a copper-clad laminate comprising an insulation layer and copper foil, using a resist liquid ejected from a liquid-jet head, and a resist layer having the desired pattern is then formed by curing the patterned resist liquid.
Japanese Patent Application Publication No. 9-8436 describes a method of manufacturing a printed circuit board by means of an inkjet type method, in which: the thickness of a resist film is specified; the film thickness is predicted; nozzle control data is created to control the nozzle in such a manner that the film thickness becomes a desired value; and the resist application step is controlled in such a manner that resist is applied separately to each circuit substrate in accordance with the nozzle control data. The operation of predicting the thickness of the resist film comprises the steps of storing data on the relationship between the nozzle shape and the film thickness, calculating the film thickness created by each spraying action for a designated resist pattern shape, from the stored relationship data, and calculating the number of application actions required to form the specified film thickness, from the film thickness per action, in such a manner that the resist film assumes the desired film thickness.
However, the resist layer must have a prescribed thickness, but in a liquid-jet system, it is generally difficult to form a thick film and therefore superimposed deposition (laminated patterning) is required. In a method which acquires a prescribed film thickness by means of superimposed deposition, there is a possibility that processing time is lengthened in accordance with the number of laminating actions and therefore it is difficult to improve the productivity. Furthermore, there are limitations on the superimposition accuracy which can be achieved by mechanical scanning, and there is a possibility that it is difficult to achieve suitable accuracy in the superimposition of the laminated layers.
The invention described in Japanese Patent Application Publication No. 9-8436 makes no concrete disclosure with respect to the control of ink ejection and ink fixing when superimposing resist ink, and since landing interference occurs between mutually adjacent dots and positional divergence occurs when the resist inks are superimposed together, then it does not seem probable that a resist film of high accuracy could be obtained. Furthermore, in the invention described in Japanese Patent Application Publication No. 9-8436, time is required for the processing of each laminating action, and therefore it is difficult to improve the productivity.